Lesion diameter measurement catheter and method

ABSTRACT

The invention provides methods and apparatus for determining cross-sectional dimensions of body lumens, such as the diameter of a blood vessel. According to one exemplary method, the diameter of a blood vessel is measured by first inflating a balloon catheter within the lumen until the balloon diameter matches the lumen diameter. Inflation may be at a very low pressure and be constrained by the lumen, or may alternatively be controlled by monitoring the flow within the lumen. The balloon includes at least one measurement element which indicates the expanded balloon cross-sectional area, circumference, or diameter. Optionally, the measurement element provides a fluoroscopic, radiographic, or ultrasound indication of the cross-sectional dimension. In alternative embodiments, such dimensions may be transmitted to the distal end of the catheter, or determined after deflation and removal of the catheter.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of, and claims the benefit of priorityfrom, U.S. patent application Ser. No. 08/895,933, filed Jul. 17, 1997,which is a divisional of U.S. patent application Ser. No. 08/435,288,filed May 4, 1995, now U.S. Pat. No. 5,752,522, the full disclosures ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of medicaldiagnostics, and particularly to the field of determining physiologiccharacteristics of body lumens. In one particular aspect, the inventionprovides methods and apparatus for measuring the cross-section of adiseased vessel segment.

To properly treat many bodily diseases or abnormalities, certainphysiologic characteristics, such as the size of a particular bodymember, often need to be determined. One example is in the treatment ofvascular lesions, stenosed regions, and particularly vascular aneurysms,which often requires the endoluminal placement of tubular prostheses,such as grafts, stents, and other structures. Before the prothesis isplaced in the vascular anatomy, the size of the lesion is measured sothat a properly sized prosthesis can be selected.

Vascular aneurysms are defined as the abnormal dilation of a bloodvessel, usually resulting from disease and/or genetic predispositionwhich can weaken the arterial wall and allow it to expand. Whileaneurysms can occur in any blood vessel, most occur in the aorta andperipheral arteries, with the majority of aortic aneurysms occurring inthe abdominal aorta, usually beginning below the renal arteries andoften extending distally into one or both of the iliac arteries.

Aortic aneurysms are most commonly treated in open surgical procedureswhere the diseased vessel segment is by-passed and repaired with anartificial vascular graft. Recently, methods for endovascular graftplacement for the treatment of aneurysms have been proposed. One suchmethod and apparatus for endovascular placement of intraluminalprostheses, including both grafts and stents, is described in co-pendingU.S. patent application Ser. No. 08/290,021, filed Aug. 12, 1994, thedisclosure of which is herein incorporated by reference. A suitableintraluminal prosthesis for such a method includes a radiallycompressible, tubular frame having a proximal end, a distal end, and anaxial lumen therebetween. The prosthesis is delivered to the area ofinterest via a delivery catheter. The prosthesis is then partiallyreleased from the catheter into a blood vessel or other body lumen toallow the prosthesis to radially expand and conform to the interiorsurface of the lumen being treated. The prosthesis can then berepositioned by the catheter until it is properly placed within thevessel. Optionally, the prosthesis may be implanted within a vessel byexpanding a malleable portion of the prosthesis with a balloon catheter.Exemplary graft prostheses are described in co-pending U.S. patentapplication Ser. No. 08/255,681, the disclosure of which is hereinincorporated by reference.

As previously described, before the endoluminal placement of anintraluminal prosthesis, it is desirable to first determine theappropriate size for the expanded prosthesis so that the prosthesis willproperly fit within the body lumen. For instance, in the case ofvascular aneurysms, it is often desirable to determine the diameter ofthe vessel adjacent to the aneurysm so that the prosthesis will matchthe size of the vessel on either side of the diseased area. In othercircumstances, the cross-sectional area or the circumference of a lumenwould be helpful. For example, where a prosthesis will conform to avessel which has an irregular cross-section, it is desirable that theperiphery of the implanted prosthesis match the lumen circumference toseal along the periphery. Alternatively, the open cross-section areawould be helpful in determining whether placement of a prosthesis is anappropriate therapy for a stenosed lumen. As a final example, it isdesirable to select a properly sized balloon catheter to firmly implantthe prosthesis within the vessel, but which will not over-expand theprosthesis and damage the healthy vessel walls.

Current methods for measuring the open cross section near an effectedbody lumen employ fluoroscopy. To determine the diameter of a vesselusing fluoroscopy, a catheter is inserted into the vessel and a contrastagent is injected into the vessel through the catheter. The blood flowcarries the contrast agent along the vessel so that the vessel can beradiographically imaged with a fluoroscope. The fluoroscope produces aplanar (or two dimensional) image of the vessel which can be evaluatedto determine the existence of a diseased or abnormal area within thevessel. The nominal diameter of the diseased or abnormal area is thenestimated by measuring the diameter of the vessel in the area adjacentto the diseased area on the radiographic image. However, such ameasurement is typically not particularly accurate since it relies ondiscerning an ill-defined boundary in a single plane. Such a measurementdoes not take into account that the vessel is usually not in the sameplane as the resulting fluoroscopic image. Another drawback to suchprocedures in determining the diameter of a vessel is that the vessel isoften irregular in cross section, i.e., is not circular. Hence, even ifthe vessel were in the same plane as the resulting fluoroscopic image ofthe vessel, it would still be difficult to measure the open diameter ofan irregular vessel.

Alternative prior art methods for measuring physiologicalcharacteristics of lumens have stressed the diseased lumen beingmeasured. To determine lumen wall compliance and internal diameter, ithas been proposed that a balloon be inflated with relatively lowpressure fluid within a lumen. By monitoring inflation fluid volume andpressure, wall compliance of an expanding lumen can be determined. Byinflating the balloon with sufficient internal pressure to expand theballoon so that it is restrained by the lumen wall, lumencross-sectional area or diameter can also be measured. However, theballoon must be inflated with sufficient pressure to ensure that it hascontacted the lumen wall all along the periphery to obtain an accuratemeasurment. Additionally, the measurement balloon systems of the priorart have utilized generally cylindrical balloons of non-compliantmaterials. Hence, the prior art methods have stressed the target regionof the diseased lumen by forcing irregular lumens towards a cylindricalshape and by distending the diseased lumen.

Improper determination of the vessel size can result in the selection ofa prosthesis that is too small and hence cannot be properly grafted. Theendoluminal placement of an improperly sized prosthesis can present anumber of serious problems. One problem is that the prosthesis must beremoved from the body lumen and replaced with another that is properlysized. This can often be difficult if the prosthesis has been radiallyexpanded while in the body lumen. To remove the expanded prosthesis, theprosthesis must be radially compressed and then withdrawn from the bodylumen. Such a procedure increases the risk of injury to the patient aswell as unduly increasing operating time and expense.

Methods and apparatus are therefore needed for accurately measuring thecross-section of a body lumen, and in particular the diameter,circumference, and cross-sectional area of a vascular lesion. In oneparticular aspect, it would be desirable to provide improved methods andapparatus for the measurement of blood vessels in the region adjacentaneurysms so that the proper size of intraluminal prostheses, such asgrafts and stents, can be accurately determined. It would be furtherdesirable if such methods and apparatus were simple to use and could beused with existing fluoroscopy technology. Finally, it would beparticularly desirable if such measurements could be taken withoutcausing unnecessary stress to the diseased vessel.

2. Description of the Background Art

As previously described, methods and apparatus for placement andrepositioning of intraluminal prostheses are described in U.S. patentapplication Ser. No. 08/290,021, the disclosure of which has previouslybeen incorporated by reference. Suitable graft structures for placementin body lumens are described in U.S. patent application Ser. No.08/255,681, the disclosure of which has previously been incorporatedherein by reference.

U.S. Pat. No. 5,275,169 describes methods and apparatus for determiningthe internal cross-sectional area and compliance of a vessel bymeasuring the volume and pressure of an incompressible fluid within aninflated balloon catheter. U.S. Pat. No. 4,651,738 describes a systemfor monitoring the pressure-volume relationship during conventionalangioplasty procedures. U.S. Pat. No. 5,171,299 describes a similarapparatus which displays balloon pressure and diameter based on internalballoon pressure during angioplasty. U.S. Pat. No. 5,135,488 describesan angioplasty system having a microprocessor for controlling,monitoring, displaying, and recording balloon inflation data. Themedical literature also describes such measurements. See, for example,Abele (1980) AJR 135:901-906; Dembe et al. (1991) J. Am. Coll. Cardiol.18:1259-1262. The use of computer enhanced radiographic imagingtechniques for determining vascular lumen diameter is described inSerruys et al. (1984) Am. J. Cardiol. 54:482-488; and Nicols et al.(1984) Circulation 69:512-522.

SUMMARY OF THE INVENTION

The present invention provides methods and apparatus for determining across-sectional dimensions of body lumens, and particularly fordetermining the cross-sectional area, circumference and diameter oftarget regions within body lumens. Body lumens amenable to the methodsand apparatus of the present invention include blood vessels, theintestines, the urethra, and the like. Although suitable for themeasurement of most body lumens, the present invention will find itsgreatest use in the measurement of vascular lesions, particularlyvascular aneurysms, vascular stenoses, and the like. Advantageously, thecross-sectional dimensions of such lesions can be used to select theproper size of intraluminal prostheses, such as grafts and stents, theproper balloon for balloon angioplasty procedures, and the propertherapy for that vascular lesion.

The methods of the present invention are carried out without disruptingthe cross-sectional characteristics being determined. According to thepresent methods, a balloon catheter is inflated within a diseased lumenso that a cross-section of the balloon substantially matches thecross-section of the lumen being measured. The present methods thenmeasure a cross-sectional dimension of the balloon within the lumen. Asused herein, "cross-sectional dimension" includes all physicaldimensions of the body lumen which relate or correspond to thecross-sectional area, specifically including the cross-sectional area,peripheral length (e.g. circumference), width (e.g. diameter in circularvessels), and the like. Advantageously, the present methods areperformed without significantly distending the diseased lumen prior toselection and application of an appropriate therapy.

The present invention may advantageously be used with other apparatusand methods for measurement of the length of vascular lesions, asdisclosed in copending U.S. patent application Ser. No. 08/380,735(Attorney Docket No. 16380-16), the disclosure of which is hereinincorporated by reference.

Broadly, the present method for measuring a cross-section of a lumencomprises inserting a balloon catheter into the lumen, and aligning theballoon with a target location of the lumen. The balloon is theninflated so that a cross-section of the balloon is substantially thesame as the cross-section of the target location of the lumen. Across-sectional dimension of the inflated balloon is then measured,providing the corresponding dimension of the target location of thelumen.

Advantageously, the methods of the present invention avoid thedistending of the lumen required for the pressure/volume monitoringmethods of the prior art. Instead, the present methods measure a lumencross-sectional dimension from a balloon inflated so as to have across-section that is substantially the same as the lumen beingmeasured, i.e. with minimal or no luminal distension. As used herein,"substantially the same" is used to mean that the balloon cross-sectionconforms to the lumen cross-section without substantially altering thecross-sectional shape or any cross-sectional dimension. Preferably, theballoon changes the measured cross-sectional width by less than 5%,ideally by less than 2%.

In one aspect of the present lumen measurement method, the peripheralsurface of the balloon is conformed or matched to the lumen based on achange in a flow through the lumen. The change is preferably measured bya sensing a change in the flow as the balloon is expanded, preferablywith a sensor on the catheter. The expansion can thus be terminatedwhen, for example, the flow is substantially blocked by the balloon,before the balloon has applied any significant force against the lumenwall.

In certain embodiments of the present method, a very flexibleelastomeric balloon is inflated using a low pressure fluid, expandingthe balloon until it is restrained by the lumen wall. The fluid is atsufficiently low pressure that it will not distend the lumen wall, whilethe elastomeric material allows the balloon to expand to conform with anirregular lumen cross-section. Preferably, an external pressure sensormeasures lumen ambient physiological pressure to limit the requiredinflation fluid pressure. The balloon thereby inflates so as to havesubstantially the same cross-section as the body lumen, withoutsubstantially expanding or otherwise traumatizing the body lumen.

Alternative embodiments of the present methods comprise expandingballoons having a conical or tapered shape with low pressure inflationfluid until a portion of the balloon having a cross-section smaller thanthe lumen is fully expanded, while a portion of the balloon having across-section larger than the lumen is not fully expanded. In suchembodiments only a portion of the balloon is matched or conformed to thecross-section of the body lumen.

As described in more detail hereinbelow, there are several alternativemethods for measuring the cross-section of the inflated balloon. Incertain embodiments of the present method, a cross-sectional dimensionof the lumen is found by deflating and removing the balloon, andmeasuring certain irreversible changes which were recorded during themaximum expansion of the balloon within the lumen. For example, aballoon having a plurality of internal segments, where each segment isattached to the inside of the balloon wall to define a balloon diameter,will record a lumen diameter by breaking those segments which areshorter than the maximum inflated balloon diameter.

Alternative embodiments of the present methods determine the expandedballoon cross-section in situ using remote electrical or mechanicalindicators. For example, a conductive coil which expands with theballoon wall will vary in electrical characteristics in correlation withballoon cross-section. Hence, measuring the resistance, inductance, orcapacitance of such an expanding conductive coil allows immediatecalculation of the inflated balloon circumference or diameter.

In further alternative embodiments, measurement elements are interpretedin situ using known imaging modalities, such as fluoroscopy,radiography, ultrasound, or the like. For example, a balloon havingelastomeric marker bands on the balloon wall are imaged while inflatedto match the lumen cross-section. Preferably, the marker bands provide asharp image, and increase in width in correlation with increasingballoon circumference, allowing calculation of the lumen circumferencefrom the marker band width. Advantageously, such marker band widthscould be accurately measured using known intravascular ultrasound (IVUS)systems from within a lumen of the catheter.

The lesion measurement catheters of the present invention comprise acatheter body having proximal and distal ends, and a balloon disposed atthe distal end of the body. The present catheters will usually includemeans for matching an inflated diameter of the balloon with a diameterof a target location of a lumen, as described above. Preferably, thepresent catheters also include a measurement element for measurement ofthe inflated balloon.

Several alternative embodiments of the measurement element aredescribed. In a preferred embodiment, the balloon is elastomeric andincludes an external pressure sensor which indicates the pressure on theouter surface of the catheter. Optionally, an internal pressure sensormeasures the pressure of an inflation fluid within the inflated balloon.The diameter of an elastomeric balloon can be correlated from adifference in these two pressures. Alternatively, monitoring the volumeof an incompressible inflation fluid allows calculation of thecross-sectional area of the inflated balloon. Advantageously, theexternal pressure sensor can also measure changes in the flow throughthe lumen to indicate when the balloon has fully matched or conformed tothe lumen cross-section, as described above.

In certain embodiments the measurement element will comprise markerbands to provide an indicator of the balloon's cross-section.Optionally, the marker bands are visible using known imaging techniques,including fluoroscopy, intravascular ultrasound (IVUS), and the like.Preferably, the marker bands are elastomeric and increase in width asthe balloon expands, as described above. Alternatively, the marker bandsare conductors which change in electrical property as the balloonexpands.

Alternative embodiments of the present measurement catheter comprise aballoon and an electrical coil attached to the balloon wall so as toexpand the coil as the balloon inflates. Electrical properties of such acoil will vary with balloon cross-sectional dimension.

Further alternative embodiments of the present catheter provide amechanical measurement of the balloon diameter or circumference.Optionally, a linkage assembly expands to measure the internal balloondiameter. Alternatively, an inelastic coil which expands with theballoon will unwind with an increasing balloon circumference. Suchmechanical measurements are optionally imaged using fluoroscopy, X-ray,or ultrasound, or alternatively are transmitted along the catheter body.

Still further embodiments of the present lesion measurement catheterinclude at least one measurement element which is altered by expansionof the balloon within the lumen. Optionally, a plurality of segments ordisks corresponding to varying balloon diameters are provided, at leastone corresponding to a diameter larger than the lumen and at least onecorresponding to a diameter smaller than the lumen. The image of thesegments or disks may change under fluoroscopy or ultrasound when aballoon diameter exceeds a corresponding segment or disk diameter.Alternatively, irreversibly overexpanded segments or disks may recordthe maximum expanded diameter of the balloon after the catheter has beendeflated and removed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a first embodiment of a lumenmeasurement catheter according to the present invention. The catheter isshown with the balloon inflated within a body lumen.

FIG. 2 illustrates the catheter of FIG. 1 in a measuring position.

FIG. 3 illustrates a particular embodiment of the present catheterhaving elastomeric marking bands.

FIG. 4 illustrates the catheter of FIG. 3 with the balloon inflated.

FIG. 5 illustrates an alternative embodiment of the present catheterhaving bands which vary in resistance with balloon circumference.

FIG. 6 is an interior view of the catheter of FIG. 5 with the balloonexpanded.

FIG. 7 illustrates an embodiment of the present catheter having anelectrical coil which expands with the balloon.

FIG. 8 illustrates a mechanical linkage which is attached to opposingsides of the inner surface of an alternative embodiment of the presentcatheter.

FIG. 9 illustrates an embodiment of the present lesion measurementcatheter having a flexible conduit attached to the balloon and aninelastic wire disposed within the conduit.

FIG. 10 illustrates an embodiment of the present catheter having aplurality of measurement elements.

FIG. 11 illustrates an embodiment of the present catheter having atapered balloon and a plurality of measurement elements.

FIG. 12 illustrates an embodiment of the present catheter having asegmented balloon with rupture disks between segments.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

The present invention provides methods and apparatus for determiningcross-sectional dimensions, such as the internal diameter,circumference, or cross-sectional area, of a body lumen. The methods andapparatus will preferably be used to measure the cross-section ofvascular lesions, and will find its greatest use in measuring thediameter of vascular aneurysms and stenoses. The methods and apparatuscan also find use in measuring internal dimensions of other defects orabnormalities. Diameter and peripheral lengths provided by the presentinvention will be particularly useful in sizing intraluminal prostheses,such as vascular grafts or stents, that are endovascularly placed withinthe vessel to treat the aneurysm or other abnormality. Cross-sectionalareas provided by the invention can also be used to select the properdiameter for a balloon angioplasty catheter or to size other therapeuticdevices.

An important feature of the present invention is that it allowscross-sectional dimensions to be measured regardless of the orientationof the body lumen within the body. Usually, most body lumens curvethroughout the body thereby reducing the accuracy of measurementsobtained from conventional fluoroscopy procedures which produce planarimages of the lumen. The present invention takes into consideration boththe varied orientations of body lumens within the body and theirirregular cross-sectional shapes when determining their physiologiccharacteristics. In making such determinations, the present inventioncan incorporate the use of existing fluoroscopy technology as well asexisting ultrasonic imaging technology.

An advantage of the present invention is that the distending of theabnormal or diseased body lumen, as associated with prior art lumendiameter measurements, is avoided. Instead, a cross-section of thepresent balloon catheter is matched with the lumen diameter. The ballooncross-sectional dimension can then be determined, indirectly providingthe lumen diameter. Thus, a proper therapy can be selected based on theexisting dimensions of the lumen, before those dimensions are altered.

To provide such features and advantages, the invention in one exemplaryembodiment provides a luminal lesion measurement catheter 10 as shown inFIG. 1. The catheter 10 includes an elongate tubular body 12 having aproximal end 14, a distal end 16, and a lumen 18 therebetween.Preferably, the length of tubular body 12 will be in the range fromabout 40 cm to about 200 cm. A balloon 20 is disposed about tubular body12 near distal end 16. Balloon 20 usually comprises an elastomericmaterial such as latex. In some embodiments, balloon 20 mayalternatively comprise a flexible, inelastic material such aspolyurethane, PET, or the like. Catheter 10 is seen in FIG. 1 insertedinto a body lumen 22, with balloon 20 shown in an inflatedconfiguration. Balloon 20 is expandable within lumen 22 so that theballoon cross-section matches and conforms to the lumen cross-section,but need not stress lumen 22 by expanding substantially beyond thatpoint. In this embodiment, expansion is controlled using external sensor24 attached to distal end 16 proximal of balloon 20. As balloon 20expands, occlusion of the body lumen will cause a drop in pressure and areduction in flow F. Sensor 24 may sense either pressure or flow.Regardless, the expansion of balloon 20 is terminated prior to expandingor stressing lumen 22.

Alternatively, expansion of the balloon may be stopped before the flowin the lumen is completely blocked, thereby avoiding all stress on thelumen wall, as well as the hazards of complete blockage of a lumen.Total lumen cross-section are then found by a correlation between theballoon diameter and the change in lumen flow, as measured at externalsensor 24. Similarly, bypass flow lumens (not shown) of known sizeextending from the proximal end to the distal end of the balloon mayalternatively be incorporated.

The diameter of inflated balloon 20 is then measured to determine thediameter of the lumen. The present invention provides severalalternative embodiments of balloon diameter measurement elements ormeans. Preferably, balloon 20 comprises an elastomeric balloon having aknown correlation between internal pressure and diameter. An internalpressure sensor 26 provides the internal balloon pressure, and therebyallows balloon diameter to be calculated from internal pressure.Preferably, internal pressure data is combined with external pressurefrom sensor 24 to provide the pressure difference across balloon 20. Asthe balloon diameter is most accurately determined by this difference inpressure, this combination provides a very precise indication of balloondiameter.

Optionally, monitoring the volume of an incompressible inflation fluidintroduced into catheter 10 from calibrated reservoir R allows thepresent catheter system to measure both the cross-sectional area andcompliance of lumen 22. Once balloon 20 has been matched to the lumencross-section as described above, the cross-section of the balloon maybe calculated from the inflation volume and the inflated balloon length.Clearly, such a calculation is most accurate where balloon 20 isconstructed so as to expand radially only, rather than in length.

Further inflation of balloon 20 from calibrated reservoir R will expandthe balloon outward against the lumen. Correlating the change in fluidvolume of the balloon with the change in pressure (as measured atinternal sensor 26) will allow calculation of the lumen wall resilience.An alternative apparatus and method for such a measurement is disclosedin U.S. Pat. No. 5,275,169.

FIG. 2 illustrates the lesion measurement catheter of FIG. 1 as used tomeasure a blood vessel cross-section in the region adjacent to ananeurism. Alternatively, the catheter might be used to measure thediameter of the aneurism itself, or to measure the open cross-sectionalarea of a stenosed region, or the like. Advantageously, the presentdevices and methods allow such measurements without distending orotherwise traumatizing such diseased lumens.

As shown in FIG. 2, catheter 10 has been inserted within an abnormallumen 30 and aligned with a target region 32. The diameter of targetregion 32 might, for example, be needed to determine the size of anintraluminal stent to be inserted within lumen 30. Balloon 20 is showninflated, thereby blocking a normal blood flow F. Thus the pressure andflow acting on external sensor 24 has been altered. This information istransmitted to the physician via wires 34. When flow F is completelyblocked by balloon 20, the cross-section of balloon 20 has been matchedto the cross-section of target region 32 of lumen 30.

FIGS. 3 and 4 illustrate an embodiment of the present lesion measurementcatheter having marker bands for determining the inflated ballooncircumference. Catheter 10 has a balloon 40 which is elastomeric.Balloon 40 includes two radiopaque elastomeric marker bands 42 attachedto the surface of elastomeric balloon 40. FIG. 3 illustrates balloon 40in a relaxed configuration having diameter 44, while bands 42 haverelaxed width 46. Bands 42 will vary with the peripheral length ofelastomeric balloon 40, which in turn will vary with balloon diameterwhen the balloon is not constrained. Generally, lesion measurementcatheters according to the present invention will have a relaxed orunexpanded outer diameter in the range from 2 mm to 12 mm, preferablybeing in the range from 2 mm to 5 mm.

FIG. 4 illustrates balloon 40 in an expanded configuration, having anexpanded diameter 48. Fully expanded lesion measurement balloons willhave diameters in the range from 6 mm to 45 mm, preferably being in therange from 12 mm to 32 mm. As shown here, the expanded balloon remainsunconstrained. Bands 42 of expanded balloon 40 have increased indiameter with the balloon, with a corresponding change in measured width50. However, if the balloon was constrained during expansion by a lumenwall having an irregular cross-section, it will be understood thatmeasured width 50 would vary with the balloon's circumference. Thus, acorrelation may be drawn between measured width 50, and ballooncircumference. Therefore, fluoroscopy or x-ray imaging which allowsmeasurement of measured width 50 will also provide the circumference ofexpanded balloon 40.

FIGS. 5 and 6 illustrate an embodiment of the present lesion measurementcatheter having conductor bands which vary in resistance with ballooncircumference. FIG. 5 shows catheter 10 having balloon 60 with threeelastomeric resistors 62. Resistors 62 are formed of a polymer or otherelastomer having known conductive properties. Suitable materials willchange in resistance in a predictable manner during elongation, such aspolyisoprene with carbon black dispersion or polysiloxane foam withgraphite impregnation.

FIG. 6 provides a cut-away view of the interior of balloon 60 in anexpanded configuration. Elastomeric resistors 62 each have a gap 64defining two resistor ends. A wire 66 is attached to each end of theresistor, and extends down the catheter body. As balloon 60 expandswithin the lumen, elastomeric resistors 62 predictably increase inlength and resistance. Measurement of the electrical resistance whileballoon 60 is expanded within the lumen allows calculation of theperipheral length of the expanded balloon. Alternatively, the resistorsmay be elastomeric segments which are attached to opposite sides of theinner balloon surface to define a diameter. Advantageously, the multipleresistors of this embodiment may be used to provide information onballoon cross-section in more than one target location.

FIG. 7 illustrates an alternative embodiment of a lesion measurementsystem in which balloon cross-section is measured based on changes inthe electrical properties of a coil. A balloon 70 has a coil 72 whichexpands with the inflated balloon wall. Coil 72 may be elastomeric ormay alternatively be a flexible wire riding in an elastomeric conduit,as will be described in regard to FIG. 9. Regardless, as the balloon isinflated, the electrical properties of coil 72 will change predictably.In some embodiments, a central wire 74 may be attached to the distal endof coil 72. The balloon circumference and diameter may be correlatedfrom the coil resistance, inductance, or capacitance. Once again, a pairof wires 76 allow measurement while the catheter is inflated within thelumen.

FIG. 8 illustrates a mechanical linkage for directly measuring balloondiameter in a further alternative embodiment of the present lesionmeasurement catheter. A balloon 80 contains a linkage 82 which is bondedto two pads 84 on opposite sides of the inner surface of balloon 80,thereby defining a diameter. Pads 84 support four equal length links 86which are rotatably joined to form a parallelogram. A diagonal link 88defines a diagonal of the parallelogram, and is held by a pivot at oneend while the other end slides in a sleeve 90. The length of theparallelogram diagonal varies with balloon diameter, allowing balloondiameter to be read from the location of sleeve 90 relative to a set ofcalibrated radiopaque marking 92 on diagonal link 88. Balloon diametercould be read by fluoroscopy, for example. Alternatively, the diagonallink might extend down the catheter body to be read from a calibratedscale at the proximal end of the catheter. Clearly, a wide variety ofalternative mechanical linkages could be used.

FIG. 9 illustrates a further embodiment of the present lesionmeasurement catheter comprising a balloon 100 and a flexible, inelasticcoil 102. Preferably, coil 102 is disposed within an open elasticconduit 104, which is bonded to balloon 100. As balloon 100 expands,conduit 104 increases in length, causing coil 102 to unwind. Preferably,one end of the coil is fixed within the conduit, allowing the peripherallength of the conduit to be determined by the position of the free end108. Optionally, the coil may be formed of a material which provides asharp image, allowing the coil windings or end position to be monitoredby fluoroscopy, radiography, or ultrasound. Alternatively, where thedistal end of the coil is fixed, the coil may extend down the catheterto provide an indication of the balloon circumference at the proximalend.

As can be seen in the embodiment of FIG. 9, the catheters of the presentinvention may advantageously include at least one lumen extendingthrough the balloon. Such a lumen may provide access for a guide wirefor repositioning the balloon, or other know intravascular devices.Preferably, such a lumen may allow introduction of an ultrasonicintravascular probe, as is shown in copending patent application Ser.No. 08/380,735 (Attorney Docket No. 16380-16), previously incorporatedby reference. A separate inflation lumen may also be provided (notshown).

FIG. 10 illustrates a still further embodiment of the present lesionmeasurement catheter, in which a balloon 110 has a plurality ofmeasurement elements of varying length. The measurement elements may bein the form of segments attached to opposite sides of the balloon wallto define a plurality of diameters. Alternately, the elements may bedisks or the like. At least one smaller segment 112 corresponds to adiameter smaller than the diameter of the target region of a lumen 114to be measured, while at least one larger segment 116 is longer. Asballoon 110 is inflated to match the body lumen diameter, smallersegments 112 will be broken, while larger segments 116 remain intact.Optionally, the segments would be of a type which would allowvisualization by known visualization modalities. Alternatively, themaximum diameter of the inflated balloon can be determined or confirmedafter the catheter is removed.

FIG. 11 illustrates a lesion measurement catheter having a conicalballoon 120. A plurality of measurement elements are provided, which maybe similar to those described regarding FIG. 10, or may advantageouslybe simple marker rings which provide an image under fluoroscopy orultrasound, optionally comprising gold or barium sulfate. Once again, atleast one smaller ring 122 and at least one larger ring 124 areprovided. Preferably, balloon 120 is inelastic, and is allowed to expandunder low pressure until restrained by a lumen 126, as described above.The smaller rings 122 are fully expanded, while larger rings 124 arenot. When visualized, the image of smaller rings 122 are straight andcrisp, while larger segments 124 are wavy and indistinct.Advantageously, such a balloon would not suffer irreversible changes,and would therefore be reusable.

FIG. 12 illustrates a final embodiment of the present lesion measurementcatheter, in which a flexible segmented balloon 130 includes a pluralityof bursting disks 132 of varying sizes. Each disk sequentially burstsunder tension as the segments expand under low pressure to fill a bodylumen 134. Segments larger than the lumen do not rupture theirassociated disks, as the lumen walls absorb the outward load. The lumendiameter is thus between the largest burst disk and the smallest intactdisk. The intact disks optionally prevent the inflation fluid fromflowing into the next larger segment, allowing balloon diameter to bemeasured by incremental fluid volume. Preferably, a radiopaque fluid isretained behind the intact disks, providing a clear indication of thelumen diameter by the number of filled segments, as seen underfluoroscopy, radiography, or ultrasound.

Although the foregoing invention has been described in some detail byway of illustration and example, for purposes of clarity ofunderstanding, it will be obvious that certain changes and modificationsmay be practiced within the scope of the appended claims.

What is claimed is:
 1. A method for measuring a cross-sectionaldimension of a target location of a body lumen, the methodcomprising:inserting a catheter into the body lumen, wherein thecatheter includes a balloon; aligning the balloon with the targetlocation within the body lumen; inflating the balloon within the bodylumen so that a cross-section of the balloon substantially matches thecross-section of the body lumen; and measuring a cross-sectionaldimension of the balloon, wherein the cross-sectional dimension of theballoon corresponds to a cross-sectional dimension of the targetlocation of the body lumen.
 2. A method as claimed in claim 1, whereinthe measuring step comprises removing the balloon and determiningirreversible changes in the balloon, wherein the changes correspond to amaximum inflated cross-sectional dimension.
 3. A method for measuring across-sectional dimension of a target location of a body lumen, themethod comprising:inserting a catheter into the body lumen, wherein thecatheter includes a balloon having, when fully expanded, a smallerportion which is smaller than the body lumen and a larger portion whichis larger than the body lumen; aligning the balloon with the targetlocation within the body lumen; inflating the balloon at low pressureuntil the smaller portion is fully expanded and the larger portion isrestrained by the body lumen; and measuring a largest fully expandeddiameter of the balloon.
 4. A method as claimed in claim 3, wherein theballoon includes a plurality of elements having distinct images when acorresponding cross-section dimension of the balloon is fully expanded,and wherein the measuring step comprises fluoroscopically orultrasonically imaging the inflated balloon within the lumen anddetermining which of the elements have distinct images.
 5. A method formeasuring a cross-sectional dimension of a target location of a bodylumen, the method comprising:inserting a catheter into the body lumen,wherein the catheter includes a balloon; aligning the balloon with thetarget location within the body lumen; inflating the balloon within thebody lumen so that a cross-section of the balloon substantially matchesthe cross-section of the body lumen; measuring a cross-sectionaldimension of the balloon while the balloon remains within the bodylumen, wherein the cross-sectional dimension of the balloon correspondsto a cross-sectional dimension of the target location of the body lumen.